Polyimides, in particular polyetherimides (PEI), are amorphous, transparent, high performance polymers having a glass transition temperature (Tg) of greater than 180° C. Polyetherimides further have high strength, toughness, heat resistance, and modulus, and broad chemical resistance, and so are widely used in industries as diverse as automotive, telecommunication, aerospace, electrical/electronics, transportation, and healthcare.
Dielectric materials for use in circuit materials and circuit boards have been the subject of intensive research and development. Nonetheless there remains a continuing need in the art for improved dielectric compositions. In many electronic applications, the electronic components frequently generate heat, and it is desirable that the circuit board contribute to heat dissipation. Such materials should further have improved heat conductivity and be tolerant of high processing temperatures, soldering temperatures, and operating temperatures, since a thermal gradient will usually exist between the warmer interior of the equipment and the ambient surroundings. Preferred materials would thus possess high heat resistance, excellent dimensional and thermal stability, and chemical resistance. Preferred materials should further exhibit excellent electrical properties, including a high use temperature, high processing/soldering temperature, a low dielectric constant, good flexibility, and adhesion to metal surfaces. It would be a further processing advantage if the dielectric compositions could be directly cast on the metal layer by solvent casting, or extruded into films using solvent-free processes such as melt extrusion. Preferred dielectric compositions can further comprise thermally conductive or electrically conductive fillers, and the dielectric layer should be relatively thin (<100 micrometers) for good heat conductivity.